“You are sure your enemy is stupid because he doesn't do things as you would do them. It will make you careless, and your enemy will surprise you.”

1990s, Long Walk to Freedom (1995)

Variant translations
If you know others and know yourself, you will not be imperiled in a hundred battles; if you do not know others but know yourself, you win one and lose one; if you do not know others and do not know yourself, you will be imperiled in every single battle.
Know your enemy and know yourself, find naught in fear for 100 battles. Know yourself but not your enemy, find level of loss and victory. Know not thy enemy nor yourself, wallow in defeat every time.
Literal translation: Know [the] other, know [the] self, hundred battles without danger; not knowing [the] other but know [the] self, one win one loss; not knowing [the] other, not knowing [the] self, every battle must [be] lost.
Source: The Art of War, Chapter III · Strategic Attack

1950s, Loving Your Enemies (November 1957)
Context: Another way that you love your enemy is this: When the opportunity presents itself for you to defeat your enemy, that is the time which you must not do it. There will come a time, in many instances, when the person who hates you most, the person who has misused you most, the person who has gossiped about you most, the person who has spread false rumors about you most, there will come a time when you will have an opportunity to defeat that person. It might be in terms of a recommendation for a job; it might be in terms of helping that person to make some move in life. That’s the time you must not do it.

Source: Last Sacrifice

Source: The Sayings and Teachings of the Great Mystics of Islam (2004), p. 28

1950s, Loving Your Enemies (November 1957)
Context: The Greek language comes out with another word for love. It is the word agape. …agape is something of the understanding, creative, redemptive goodwill for all men. It is a love that seeks nothing in return. It is an overflowing love; it’s what theologians would call the love of God working in the lives of men. And when you rise to love on this level, you begin to love men, not because they are likeable, but because God loves them. You look at every man, and you love him because you know God loves him. And he might be the worst person you’ve ever seen. And this is what Jesus means, I think, in this very passage when he says, "Love your enemy." And it’s significant that he does not say, "Like your enemy." Like is a sentimental something, an affectionate something. There are a lot of people that I find it difficult to like. I don’t like what they do to me. I don’t like what they say about me and other people. I don’t like their attitudes. I don’t like some of the things they’re doing. I don’t like them. But Jesus says love them. And love is greater than like. Love is understanding, redemptive goodwill for all men, so that you love everybody, because God loves them. You refuse to do anything that will defeat an individual, because you have agape in your soul. And here you come to the point that you love the individual who does the evil deed, while hating the deed that the person does. This is what Jesus means when he says, "Love your enemy." This is the way to do it. When the opportunity presents itself when you can defeat your enemy, you must not do it.

Source: Station Eleven (2014), Chapter 23 (p. 139)

Source: Lullaby (2002), Chapter 22

Source: Economic Warfare Quotes